It's not too late at all, Zoltan. We're still polishing the app, so there is no need to rush. Since this is just to apply, don't feel obligated to invest too much of your time.
Nutritious, we are taking a flexible approach with the selected artist(s). We're looking for sound that really brings the art style to life. Music doesn't have to be anything long or elaborate, and while custom music/sfx are always nice, we will accept stock assets you might have made if they fit the game right. Basically, we'll review the submissions and say "we want you to organize the sounds and flesh this out", or "can we get two more 45sec tracks from you" and just pay everyone accordingly. The total assets we're looking for are:
one song for the menus
one song for gameplay, possibly 6 (one for each difficulty) if there are multiple great submissions
sfx for the menus (touch object, slide object, object appear, object disappear)
sfx for the game (bomb appear, defuse, detonate, score bump, grade up, color shift, bomb power up
Of course, we have more information to share, but this should be enough to give you an idea of the scope of the work. If you have a standard rate, please include it with your submission, along with any details you want to share about the work. For example, if you look at the Space Invaders video, each level has different music and sound effects that compliment the music. That would be an interesting creative touch that we are willing to entertain.